1. Field of the Invention
The present invention relates to a display device, and in particular, a driving circuit for an electric charge recycling Thin Film Transistor-Liquid Crystal Display (TFT-LCD) and a method thereof.
2. Background of the Related Art
As shown in FIG. 1, the conventional TFT-LCD driving circuit includes an LCD panel 10 having a plurality of pixels at the intersections of a plurality of gate lines GL and a plurality of data lines DL. A data driving unit 20 provides pixels with a signal, such as a video signal, through the data lines DL of the LCD panel 10, and a gate driving unit 30 selects a corresponding gate line GL of the LCD panel 10 and turns on a corresponding pixel.
The pixels are configured by a plurality of thin film transistors 1, each gate is connected with a corresponding gate line GL and each drain is connected with a corresponding a data line DL. A storing capacitor Cs and an LCD capacitor Clc are connected in parallel with the source of the thin film transistor 1.
A shift register (not shown) of the data driving unit 20 sequentially provides video data by one pixel, and a video data corresponding to the data line DL is stored. The gate driving unit 30 outputs a gate line selection signal GLS and selects a corresponding gate line GL from a plurality of gate lines GLn. The thin film transistors connected with the selected gate line GL are turned on, and the video data stored in the shift register (not shown) of the data driving unit 20 is applied to the drain, so that the video data are displayed on the LCD panel 10. When the above-described operations are repeatedly performed, the video data are displayed on the LCD panel 10.
At this time, the data driving unit 20 provides a VCOM, a positive video signal and a negative video signal to the LCD panel 10, so that the video data are displayed on the LCD panel 10. As shown in FIG. 2, in the conventional art, when the TFT-LCD driving circuit is driven, the positive video signal and the negative video signal are alternatively applied to the pixels whenever the frames are changed so that the LCD does not receive a DC voltage. Therefore, VCOM, which is an intermediate or a median voltage level between the positive video signal and the negative video signal, is applied to the electrode of the TFT-LCD upper plate.
When alternatively applying the positive video signal and the negative video signal to the LCD with respect to VCOM, a light transfer curve of the LCD is not identical, thus causing a flicker problem. In order to prevent the flicker problem, as shown in FIG. 3, the frame inversion method, the line inversion method, the column inversion method and the dot/pixel inversion method are used.
Namely, FIG. 3A illustrates the frame inversion method in which the polarity of a video signal is changed whenever the frame is changed, and FIG. 3B illustrates the line inversion method in which the polarity of a video signal is changed only whenever the gate line GL is changed. In addition, FIG. 3C illustrates the column inversion method in which the polarity of a video signal is changed whenever the data line DL and the frame are changed. FIG. 3D illustrates the dot inversion method in which the polarity of a video signal is changed whenever the gate line GL, data line DL and frame are changed.
At this time, the quality of the picture is increased using the frame inversion, the line inversion, the column inversion and the dot inversion, which is listed in order from lowest to highest quality. The number of the polarity changes is increased proportionally to the quality of the picture, thus increasing the power consumption. Such power consumption increase is undesirable.
For example, FIG. 4 illustrates a waveform of the odd number of the data lines DL and the even number of the data lines DL inputted into the LCD panel 10 in the dot inversion method. Namely, the polarity of the video signal of the data line DL is changed with respect to VCOM whenever the gate line GL is changed.
At this time, assuming that the entire portion of the TFT-LCD panel is gray color, the video signal variation width V of the data line DL becomes two times the VCOM and the variation width of the positive video signal or the VCOM and the variation width of the negative video signal. In addition, assuming that the capacitance of the data line DL is C.sub.L, the power consumption of the output terminal is computed by the following equation. EQU P=V.sub.DD .multidot.I.sub.ave =V.sub.DD (C.sub.L .multidot.V.multidot.F.sub.reqGL)
Where, a V.sub.DD is the power supply voltage, and a F.sub.reqGL is a gate line frequency.
Since the video signal is changed from positive to negative or from negative to positive whenever the gate line GL is changed, the power consumption is increased in the dot inversion method. Therefore, when fabricating the LCD device using a polycrystal silicon thin film transistor (Poly-si TFT), a large amount of heat is generated due to a high power consumption, so that there is a characteristic degradation of the LCD device.